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In this work, the microstructure of titania coating fabricated on the surface of hydrostatically extruded titanium grade 4 with the use of the micro-arc oxidation method was studied. The surface topography and microstructure investigations performed with atomic force microscopy and scanning and transmission electron microscopy revealed that, by using an Na₂HPO₄ electrolyte, a well-adherent porous coating is produced on the top surface and side walls of the extruded rod. The distribution of chemical elements was analyzed by using energy dispersive X-ray spectroscopy. The chemical elements dissolved in the electrolyte (Na, P and O) incorporated into the coating. Sodium locates preferentially in the outer part of the coating, while phosphorus and oxygen are distributed throughout the whole coating. The most relevant finding shows that a grain refinement caused by a hydrostatic extrusion provoked an increase in …